770 as a link for Topfield ?
 

is it in theory possible to utilize 770 as a link for Topfield 5100? My idea would be to connect 770 to Toppy with usb, connecting to 770 by ftp and transfering files with wlan to pc

In theory, yes. In practice it might not be... practical.

Toppy hard drive is seen as a usbdisk, if I remember correctly. So using the 770 in usb host mode with the usb-power-injector (at least Thoughtfix has been doing this) you could probably mount Toppys hard drive on the 770. Then it's just a matter of installing ssh on the 770, and using scp to transfer files between the PC and 770...

I bet it would be easier to get a long enough usb cable to reach your computer...